An inertial force sensor, such as an angular velocity sensor and an acceleration sensor, detects angular velocity, acceleration, or both of them.
In order to detect axial components of an acceleration along an X-axis, a Y-axis, and a Z-axis which are perpendicular to each other, total three acceleration sensors: an acceleration detector element for detecting acceleration in a direction of the X-axis; an acceleration detector element for detecting acceleration in a direction of the Y-axis; and an acceleration detector element for detecting acceleration in a direction of the Z-axis. Angular velocities about the axes can be detected by total three angular-velocity detector elements: an angular-velocity detector element for detecting angular velocity about the X-axis; an angular-velocity detector element for detecting angular velocity about the Y-axis; and an angular-velocity detector element for detecting angular velocity about the Z-axis.
It is, however, difficult to reduce the size of a sensor which includes plural detector elements that detect acceleration in plural axis directions and angular velocities about plural axes.
Patent Literature 1 discloses a conventional inertial force sensor in which one detector element detects acceleration in plural axis directions or angular velocities about plural axes. This inertial force sensor includes a weight, a fixing portion for holding the weight, and a coupling portion for connecting the weight to the fixing portion. The weight has a mass large enough to detect inertial forces. The coupling portion has flexibility and detects the inertial forces based on deformations thereof or variations in location of the weight, which are caused by the inertial forces applied to the weight.
Patent Literature 2 discloses a conventional vibration-isolation structure of an inertial force sensor that detects angular velocities. The vibration-isolation structure includes an elastic body that can easily warp in a direction in which a Coriolis force occurs.
In the conventional inertial force sensors described above, it is difficult to provide a vibration-isolation structure for one detector element that detects angular velocities about plural axes. For example, while the weight of the detector element is driven to vibrate in an X-axis direction, an angular velocity about a Z-axis generates a Coriolis force which acts on the weight in a Y-axis direction to cause a coupling portion to deflect. The angular velocity about the Z-axis is detected based on the deflection. However, the angular velocity may be erroneously detected in the case where the weight is subjected to an inertial force caused by external impacts or vibrations, thereby resulting in a deflection of the coupling portion in the Y-axis direction. To prevent such erroneous detection of angular velocity, it is necessary to provide the inertial force sensor with a vibration-isolation structure against external impacts and vibrations. In this case, the vibration-isolation structure is designed to decrease vibrations in the Y-axis direction, which requires that a supporting member for supporting the detector element be easy to deflect in the Y-axis direction. However, such a vibration-isolation structure of conventional inertial force sensors can hardly prevent vibrations not only in the Y-axis direction but also in plural axis directions, such as the X-axis and Z-axis directions.